In the field of coaxial electric signal cables there is voluminous prior art on variations of construction and composition of the center signal conductor, the insulation, also called the dielectric, the coaxial shielding, and the optional protective outer jacket of the cables.
Continuing efforts are made to provide a cable having the best electrical characteristics, the lightest weight, the greatest flexibility, and the smallest size possible. These qualities along with the best economy of manufacture are needed considering the necessary qualities the cable must have to be useful to meet the increasingly high specifications necessary for application in modern electronic apparatus, such as computers, communications satellites, inhabited space modules and space craft, and ground communications equipment.
Much improvement in cable properties has been accomplished in recent years by utilization of foamed insulation, such as foamed thermoplastic polymers and especially porous expanded polytetrafluoroethylene (ePTFE), such as that disclosed in U.S. Pat. Nos. 3,953,566, 3,962,153, 4,096,227, 4,187,390, 4,902,423, and 4,478,665 (assigned to W. L. Gore & Associates, Inc.), for example. To achieve an insulation having the lowest dielectric constant, less of these materials are required for a given dielectric constant.
Thin copper or aluminum wire tubing has been extruded around center conductors and insulation to provide shielding of the cable against outside electromagnetic field (EM) interference. Spirally wrapped metal foil and served or braided metal wires or tape also serve this purpose as does metal-plated (metallized) polymer tape wrapped spirally or cigarette wrapped around the insulation. If protection of the cable against electromagnetic interference (EMI) or electromagnetic radiation is desired, a conductive metal may be used in the shielding.
It has also become useful to bundle more than one of the cables described above together in a single cable and to include one or more optical fiber signal cables in the bundle with electric signal cables.
The present invention provides even further improvements in size, weight, and flexibility for a given level of electric signal transmission speed and quality and protection against outside interference.